DESCRIPTION: The objective of this project is to define mechanisms of catalysis and electron transfer (ET) by selected quinoprotein dehydrogenases and their physiologic protein redox partners. These proteins are being used to develop and test hypotheses concerning (I) the roles of protein-bound quinone cofactors in catalysis and ET, (ii) mechanisms of long range interprotein ET reactions, and (iii) factors which stabilize the specific interactions between soluble proteins that facilitate intermolecular ET. study of physiologic ET reactions has for the most part been limited to integral membrane proteins for which structural information is difficult to obtain. Quinoprotein dehydrogenases are soluble and have two relatively unique and interesting properties. They utilize enzyme-bound quinones as prosthetic groups, and for electron acceptors they use other proteins rather than O2 or pyridine nucleotides. We are characterizing catalytic reaction mechanisms of the quinoproteins, developing kinetic models for their ET reactions, and determining crystal structures of these proteins free and in complex with physiologic redox partners. This allows us to correlate structural information with the results of our studies. A major aim of this proposal is to use site-directed mutagenesis to test hypothesis which have been developed concerning mechanisms of catalysis, protein-protein interaction and long range ET. Elucidation of factors which influence specific protein-protein interactions between quinoproteins and their electron acceptors will provide insight into the process of protein-protein recognition which is common to a wide range of biologic phenomena. Long range ET is a process which is central to bioenergetic phenomena such as respiration and certain reactions of intermediary metabolism. Characterization of the mechanisms and pathways of long range interprotein ET will allow us to better understand these fundamental processes at the molecular level.